import java.util.*;
public class TriangleArea
{
    public static double calculateArea(double a, double b, double c)
    {
        double p = (a + b + c)/2;

        return Math.sqrt(p * (p - a) * (p - b) * (p - c));
    }

    public static void main(String[] args)
    {
        System.out.println("请输入三角形的三条边长");

        Scanner in = new Scanner(System.in);
        double a = in.nextDouble();
        double b = in.nextDouble();
        double c = in.nextDouble();

        System.out.println("边长为 " + a + ", "+ b + ", " +
                c + " 的三角形面积为 " + calculateArea(a,b,c));
    }
}
